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8998 



Bureau of Mines Information Circular/1985 




Inverted Pyramid-Shaped Plugs for Closing 
Abandoned Mine Shafts— Galena, KS, 
Demonstration Project 



By W. M. Dressel and John S. Volosin 



UNITED STATES DEPARTMENT OF THE INTERIOR 



03 

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751 

' /^INES 75TH A^ 



Information Circular 8998 



Inverted Pyramid-Shaped Plugs for Closing 
Abandoned Mine Shafts— Galena, KS, 
Demonstration Project 

By W. M. Dressel and John S. Volosin 




UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



Library of Congress Cataloging in Publication Data: 






Dressel, W. M. (W'aldemar M,) 

Inverted pyramid-shaped plugs for closing abandoned mine shafts- 
Galena, KS, demonstration site. 

(Bureau of Mines information circular ; 8998) 

Bibliography: p. 14. 

Supt. of Docs, no.: I 28.27:8998. 

1. Mine filling. I. Volosin, John S. II. Title. III. Seriest In- 
formation circular (United States. Bureau of Mines) ; 8998. 



TN2»5iiM^ [TN292] 622s [622] 84-600227 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Selection of shaft sites 3 

Design of plug 6 

Installation of plugs 9 

Backfill 11 

Installation of slab caps 12 

Discussion 13 

Conclusions 13 

References 14 

ILLUSTRATIONS 

1 . Proj ect site location 3 

2. Typical open shaft with timber still in place 4 

3. Typical open shaft with enlarged surface opening 4 

4. Typical shaft showing rotted timber and washout along timbers 5 

5. Typical open shaft showing circular outline in slumping residuum 5 

6. Installed plug 6 

7. 8-ft form showing reinforcing grid 7 

8. 10-foot form showing I-beam position and reinforcing grid 8 

9. 12-ft form showing I-beams and position of horizontal and vertical re- 

inforcing bars 8 

1 . Lowering form into opening 9 

11. Form filled with concrete showing space between form and shaft wall 10 

12. Poured plug with expanded metal edging resting on reinforcing bars 10 

13. New concrete poured on expanded metal surrounding plug 11 

14. 10-foot form showing spider-leg reinforcing over edge of form to support 

the expanded metal 12 

TABLES 

1 . Material requirements per plug 7 

2. Material requirements per slab 12 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


ft 


foot lb pound 


ft2 


square foot yd^ cubic yard 


in 


inch 



INVERTED PYRAMID=SHAPED PLUGS FOR CLOSING ABANDONED MINE 
SHAFTS-GALENA, KS, DEMONSTRATION PROJECT 

By W. M. Dressel ^ and John S. Volosin ^ 



ABSTRACT 

This Bureau of Mines report describes a shaft closure demonstration 
project in which 11 inverted pyramid-shaped plugs were used to plug 
abandoned open mine shafts in Galena, KS. The inverted pyramid-shaped 
forms, fabricated from steelplate, were designed so that the inverted 
base would be larger, by 4 ft on a side, than the approximate size of 
the shaft opening at the surface residuum-solid rock interface. 

After the surface openings of the shafts were trimmed with a backhoe, 
the steel forms, complete with reinforcing, were lowered into the open- 
ings and filled with concrete; the remaining portions of the openings 
above the plugs were backfilled to slightly above the surrounding sur- 
face level with waste rock and soil. 

Location and elevation monuments were installed for long-term evalua- 
tion of the success of the project. 



^Supervisory metallurgist. 
^Metallurgist. 
Rolla Research Center, Bureau of Mines, Rolla, MO. 



INTRODUCTION 



The Bureau of Mines operated a shaft 
closure demonstration project in Galena, 
KS, in which 11 inverted pyramid-shaped 
plugs were installed in abandoned open 
mine shafts. The primary purpose of the 
project, which was part of the Bureau's 
Conservation and Development Program for 
conserving land resources, was to provide 
alternative methods for closing some of 
the hundreds of open shafts in the area. 

The Galena field is in the Tri-State 
zinc-lead belt district of Kansas 
Missouri-Oklahoma, which was one of the 
largest zinc-lead mining districts in the 
country. The district produced over 
11 million tons of zinc and 2.8 million 
tons of lead during its 122 years of 
operation. 

Mining began in the Tri-State district 
in 1848 with the discovery of lead ores 
in Joplin, MO. Increased mining activity 
developed in the 1870*s, coincident with 
the extension of the railroad into the 
area and the development of new milling 
and smelting techniques for zinc. By 
1875, the Joplin field became the leading 
zinc producer in the Nation. Mining 
moved westward with the discovery of the 
Galena, KS, field in 1877; the Peoria, 
OK, field in 1891, and the Commerce, OK, 
field in 1905. 

Mining continued in the Missouri por- 
tion of the district until 1957 and in 
the Kansas-Oklahoma portion until 1970. 

Early mining leases were generally 
small with many leases being only 100 or 
200 ft square ih-h) .^ The ore was mined 
by small crews of men using handtools and 
simple hoisting devices. Exploration was 
done by sinking a shaft, generally 50 to 

•^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



100 ft deep, until ore was found and then 
drifting outward (_5). If drifts reached 
300 ft in length or if ventilation became 
difficult, additional shafts were sunk. 
If ore was not encountered, the miner 
moved to new ground and sank another 
shaft. In 1892, Henrich (j6) reported 
that diamond drills were being used for 
prospecting deeper than 100 ft. The 
churn drill replaced shaft sinking as the 
principal exploration tool about 1900 O, 

The use of shafts as a means of explor- 
ation and the small lease and sublease 
mining plots resulted in a high density 
of mining shafts in the area. Many of 
these shafts remain open. They are con- 
stant safety and environmental hazards 
and limit the uses for the land. 

In preparing a series of reports for 
the Bureau, the State Geological Surveys 
of Kansas, Missouri, and Oklahoma located 
over 1,400 abandoned open mine shafts in 
the Tri-State district (8-10). In the 
Galena, KS, field alone, 377 open shafts 
were located within or adjacent to the 
city limits of Galena. All but 11 of 
these shafts showed surface enlargement 
because of cribbing removal or failure. 

Backfilling is a common method for 
filling shafts and is quite successful if 
done properly with graded material free 
of degradable trash and in a manner that 
avoids temporary bridging. Wood planking 
has been used with varying degrees of 
success but eventually decays, resulting 
in an unsafe closure. Although concrete 
caps have been successful in some in- 
stances, there are examples of failed 
concrete caps in the Galena area where 
the caps were improperly reinforced or 
where undercutting around the shaft 
caused the cap to tip on end, thus creat- 
ing a hazard from an open shaft. 



In the Picher field, at least one com- 
pany successfully used concrete cubes to 
close shafts when abandoning the field. 
The cubes, which were 6-1/2 ft on a side, 
were constructed on the surface next to 
the shaft and then rolled into the open- 
ing and wedged into place by undercutting 
and blasting. 



This report describes a method using an 
inverted pyramid-shaped plug that would 
be easy to install and would seal itself 
into the shaft. The weight would be dis- 
tributed to the edges and sides of the 
shaft. 



SELECTION OF SHAFT SITES 



Galena was picked as a site for demon- 
strating methods for closing abandoned 
shafts because over 350 open shafts were 
readily accessible in a populated area. 
Before a location was selected for the 
demonstration, the Bureau contacted the 
Galena city government for its view as to 
which areas within the city limits were 
in the most need of shaft plugging. From 
the locations the city officials listed, 
the Bureau selected a site in NE1/4SW1/4 
sec. 14, T 34 S, R 25 E at the west end 
of Front, First, and Second Streets. 
Virtually all of the open mine shafts in 
Galena are on privately owned land. A 
search of the county land records was 
made to determine the ownership of the 
lands, and the owners were contacted to 
obtain grants of easement that would per- 
mit the Bureau to carry on the demonstra- 
tion project. Figure 1 shows location of 
the site and the location of the shafts 
closed during the demonstration; the 
breaks in the shaft numbering sequence 
resulted from changes in the original 
closure plan, brought about in one case 
because considerable construction debris 
had been dumped in the opening and in 
other cases because the locations were 
out of the area covered under the grants 
of easement. 

Four of the open shafts selected for 
plugging are shown in figures 2 through 
5, Contract 50/34005 was let to Goodson 
and Associates, Inc., Denver, CO, in 1982 
to obtain the shaft dimensions, assess 
the conditions of shaft side walls, and 



obtain an estimated contact between over- 
burden and solid rock. These measure- 
ments were used in preparing bid specifi- 
cations for the plug installations re- 
ported herein. Eleven shafts were 
plugged, two were capped, and one was 
backfilled during the demonstration. 





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FIGURE 1. - Project site location. 




FIGURE 2. ° Typical open shaft with timber still in place. 




FIGURE 3. = Typical open shaft with enlarged surface opening. 




FIGURE 4. ° Typical shaft showing rotted timber and washout along timbers. 




FIGURE 5. - Typical open shaft showing circular outline in slumping residuum. 



DESIGN OF PLUG 



Pyramidal-shaped plugs designed for the 
project consisted of prefabricated steel 
forms with installed reinforcing, which 
were lowered into the prepared shaft 
opening and filled with concrete. 

The shafts were roughly square and 
ranged in size from 4 to 8 ft. The forms 
for the plugs were designed so that the 
tops of the plugs were approximately 4 ft 
larger on a side than the size of the 
shaft opening. The shape of the form was 
that of an inverted 45° pyramid, A 
sketch of an installed plug is shown in 
figure 6, Of the 11 forms required for 
the demonstration, 3 were 8 by 8 ft, 6 
were 10 by 10 ft, and 2 were 12 by 12 ft. 
The 8- by 8-ft and the 10- by 10-ft forms 
were constructed of 3/16-in hot-rolled 
low-carbon steelplate welded at the 
seams. The 12- by 12-ft forms were con- 
structed of 1/4-in hot rolled low-carbon 
steel. The external edges of the seams 
were reinforced by the addition of a fab- 
ricated angle, approximately 3 in on an 
edge, welded to the seam. This rein- 
forced edge proved very beneficial since 
much of the weight of the plug rested on 
the corners before seating, 

A horizontal reinforcing rod grid was 
placed 1 ft from the top in the 8- 
ft-square pyramid forms, 1,25 ft from the 
top in the 10-ft forms, and 1.5 ft from 
the top in the 12-ft forms, A 12-in grid 
spacing was used for both east-west and 
north-south positions (fig, 7), Grade 
60, No, 7 reinforcing bars were used in 
each instance. 



In the 10-ft form, 
0.326-in web thicknes 
long were welded to 
which was welded to 
form. The beams we 
to each other and 
equidistant from the 
and from each other ( 



two S4 I-beams with 
s approximately 6 ft 
a 1/4-in footplate 
the sides of the 
re arranged parallel 
spaced approximately 
parallel side walls 
fig 8), 




12 



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A 
N 



Pier 






Surface residuum 

^■''°'Q'iTc<^'^'"->'^ 




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T 

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FIGURE 6. ■ Installed plug. 

To brace the side walls of the 12-ft 
form, two S4 I-beams , approximately 8 ft 
long with a 0,326-in web thickness, were 
welded to the form at right angles to 
each other. The ends of these beams were 
welded to a 1/2-in plate at least 1 ft 
square, which in turn was welded to a 
1/2-in plate at least 1 ft sq which, in 
turn, was welded to the inside of the 
form approximately 2 ft from the top 
(fig. 9), 

Vertical reinforcing bars were placed 
6 in from each of the sloping sides of 
the pyramidal form. They were spaced 
1 ft apart at the top of the form and ta- 
pered down to a few inches near the bot- 
tom. The top end of the rebars extended 
to within 6 in of the top of the form, A 
spacer was welded approximately 1 ft from 
the tip of each form to hold the rods 
6 in from the side walls (fig, 9), 

Material requirements per plug are tab- 
ulated in table 1, 



TABLE 1. - Material requirements per plug 



Approximate shaft size 



4 ft 



6 ft 



8 ft 



Pyramid form size ft.. 

Metal preform, f t^ . . 

Weight of metal preform lb.. 

Estimated rebars per shaft: 

Linear ft... 

Weight lb. . 

I-beam: 

Length ft. . 

Weight lb . . 

Edge angle: 

Length ft.. 

Weight lb. . 

Total weight of steel lb.. 

Concrete yd-^ . . 

'3/16-in cold-rolled , low-carbon 
^1/4-in cold-rolled, low-carbon 



8x8x4 

'90.51 

693 

327 
660 




27.7 

260 

1,613 

3.2 



10x10x5 

'141.2 

1,083 

495 
1,020 

12 
89 

34.6 

325 

2,517 

6.2 



12x12x6 

2203.6 

2,079 

698 
1,420 

16 
118 

41.6 

391 

4,008 

10.7 



steel plate, 
steel plate. 




FIGURE 7. - 8-ft form showing reinforcing grid. 




FIGURE 8. - 10-ft form showing I-beam position and reinforcing grid. 




FIGURE 9. - 12-ft form showing I-beams and position of horizontal and vertical reinforcing bars. 



INSTALLATION OF PLUGS 



The contractor, using a backhoe, 
trimmed sufficient material from around 
the surface of each open shaft to provide 
a reasonably level contact between the 
surface residuum and the bedrock. In 
several cases rock ledges or boulders 
needed to be trimmed to provide a suita- 
ble bearing surface for setting the 
forms. Trimming was done with a jackham- 
mer bit fitted to the backhoe. 



The prefabricated forms we 
to the site on a flatbed trai 
unloaded from the truck and 
rectly in the hole using a 
(fig. 10). In several cases 
sidewall trimming using the 
or jackhammer was required 
level position for the forms. 



re delivered 
ler and were 
placed di- 
1 7-ton crane 
, additional 
backhoe and/ 
to obtain a 



A 4-in pipe was positioned in the cen- 
ter of each plug and was long enough to 
extend above the surface level of the 
ground after backfilling. These pipes 



were designed to remain as reference 
markers for followup evaluation. 

Class A concrete was delivered to the 
site from a local batch plant and poured 
into the forms. The 8-ft forms each 
required 3.2 yd^ of concrete, the 10- 
ft forms 6.2 yd^ , and the 12-ft forms 
10.7 yd3. 

After the first three plugs were 
placed, it was noted that since the mine 
openings were only roughly square, there 
were noticeable gaps between the form and 
the sidewalls at some places (fig. 11). 
In these areas, reinforcing bars were 
positioned over the edge of the form and 
extended to the side of the prepared 
opening. This was covered with a 2-ft 
width of expanded metal, and 4 in of con- 
crete was poured on this expanded metal 
(fig. 12). Figure 13 shows the same hole 
after the completion of the edge pour. 





FIGURE 10. - Lowering form into opening. 



10 




FIGURE 11. - Form filled with concrete showing space between form and shaft wall. 




FIGURE 12. - Poured plug with expanded metal edging resting on reinforcing bars. 



11 




FIGURE 13. - New concrete poured on expanded metal surrounding plug, 



Before pouring concrete in the last 
eight forms , steel reinforcing rod was 
bent and fastened to the installed hori- 
zontal reinforcing grid and extended in 
spider-leg fashion several feet over the 
edge of the form. The 2-ft-wide expanded 
metal was positioned over these reinforc- 
ing rods, and concrete was poured over 
this when the form was filled. Figure 14 
shows the positioning of the spider legs 
and expanded metal. 



An additional 1 to 1-1/2 yd^ of con- 
crete was required for each shaft because 
of these modifications. 

In the installation of one 12-ft and 
one 10-ft plug, the center reinforcing 
bars were left unwelded to the sides of 
the form to allow the form to bulge along 
the edges to better fill the gaps. This 
appeared to be an effective measure. 



BACKFILL 



After a concrete curing period of at 
least 7 days, the holes were backfilled 
with waste rock available near the 
shafts. The backfill at each site was 
mounded so that the center of the fill 
was approximately 2 ft above the sur- 
rounding ground surface. The 4-in pipe 



extending from the center o.f each plug 
was trimmed so that it extended 6 in 
above the fill; it was filled with con- 
crete and will remain as a marker for 
evaluation purposes. These markers have 
been located, and elevations of their 
tops have been determined. 



12 




FIGURE 14. - 10=ft form showing spider-leg reinforcing over edge of form to support the 
expanded metal. 

INSTALLATION OF SLAB CAPS 



In some Instances, solid rock exposed 
at the surface was competent enough so 
that there was virtually no cratering or 
shaft enlargement at the surface. In 
these cases, it was found expedient to 
trim away loose surface rock 
reinforced concrete slabs, 
openings, approximately 4.5 
were closed by this method 
completion of the project. 



and install 

Two mine 

by 4.5 ft, 

during the 



The slabs were designed to extend ap- 
proximately 5 ft over each edge of the 
open mine shafts. A reinforcing grid of 
No. 7 rebars spaced 1 ft apart at the 
edges, 1/2 ft apart in the area over the 
opening, and 1/2 ft from the bottom was 
specified. Eighteen inches of class A 
concrete were poured. A 4-in pipe was 
set into the center of each grid to serve 
as a marker for future evaluation of the 



project. The material requirements for 
each poured slab are shown in table 2. 

TABLE 2. - Material requirements per slab 



Size of shaft 

Dimension of slab 

Number of No. 7 rebars 
Total length of rebars 
Total weight of rebars 
Thickness of concrete. 
Volume of concrete.... 



• • • X u • • 

• • • X u • • 



• • • X u • • 

• • .lb* • 

• • • X u • • 

..yd^.. 



4.5x4.5 

15x15x1.5 

46 

690 

1,420 

1.5 

12.5 



These slabs were of sufficient size and 
sufficiently reinforced to remain indefi- 
nitely without breaking or flipping over 
in the event of washout under part of the 
cap. They were also designed to with- 
stand loads from automobile or truck 
traffic which may occur in the area fol- 
lowing closure of the shafts. 



DISCUSSION 



13 



Working around abandoned mine shafts in 
areas where the extent of the abandoned 
underground mine working and the stabil- 
ity of the surface material around the 
shafts is not known is potentially haz- 
ardous. The contractor and suppliers 
were aware of the possible hazards and 
proceeded with due caution and regard for 
personal safety. 

A minimum of installation problems were 
involved, and only a few changes were 
necessary in completing the planned dem- 
onstration program. 

Most of the material trimmed from the 
shaft openings was allowed to fall into 
the open shafts, since sufficient waste 
rock was available on the nearby surface 
to backfill the openings over the in- 
stalled plugs. In at least one instance, 
temporary bridging of a shaft occurred 
during the trimming operation. This was 
to be expected because the material was 
ungraded, but it pointed out the neces- 
sity for using graded material when clos- 
ing small shafts by backfilling. 

In preparing hole 14 for plug installa- 
tion, the hole was found to be larger 
than original surface measurement had in- 
dicated, and it was difficult to obtain a 
stable bedrock surface. It became ap- 
parent that the alternatives were a plug 
at least 16 ft in diameter, a cap 22 ft 
in diameter, or completely backfilling 
the hole; backfilling was chosen, and ap- 
proximately 350 yd-^ of backfill were re- 
quired to close the opening. A 4-in pipe 
was also used as a marker for this 
closure. 

It also became obvious that the shaft 
dimension measurements made from the sur- 
face in these old hand-dug shafts before 
they were prepared for plugging were not 



the most reliable measurements that could 
be made. In several instances, measure- 
ments made after the holes were prepared 
required changes in plug size from origi- 
nal specifications. For example, the 
plug put in open shaft 19 was the plug 
meant to be placed in shaft 14. 

The original specification required 
that cross-reinforcing bars be welded 
near the top of each form to be used for 
attaching cables for moving the forms. 
The fabricator preferred to weld a plate 
with an eye in each corner. Figure 10 
shows this to be a preferable method and 
allowed for easy handling and positioning 
of the forms. The crossbars in the orig- 
inal design were omitted in the later- 
constructed forms. 

The reinforcing rods were welded into 
position at crosspoints, and the ends 
were welded to the sides of the forms. 
This tended to make very rigid form. The 
welding of the reinforcing rod ends at 
the center of the sides was omitted in 
several of the forms installed near the 
end of the demonstration. This enabled 
the form to bow out when filled with con- 
crete to more nearly take the shape of 
the opening. However, when this happens, 
there are no reinforcing bars in the 
bowed-out part of the plug. A modified 
design that allowed the center reinforc- 
ing bars to extend through the plug walls 
might eliminate this problem. 

Four plug forms were set in their re- 
spective shafts prior to a 7-in rainfall. 
As a result, the forms were filled with 
water and had to be pumped out before the 
concrete was poured. Small drain holes 
were left in the last three plugs in- 
stalled; however, the plugs were filled 
with concrete before the next rain. 



CONCLUSIONS 



The 11 plugs and 2 caps installed and 
the shaft that was backfilled appear to 
be effective methods for closure in the 
Galena area. Long-range evaluation of 



the closures will be necessary to prove 
the stability of the inverted pyramid 
plugs . 



14 



REFERENCES 



1. Hay, R. Geology and Mineral Re- 
sources of Kansas. KS State Bd. Agri,, 
Biennial Rep. 8, pt. 2, 1893, pp. 99-162. 

2. Clerc, F. L. The Ore Deposits of 
the Joplin Region, Mo. Trans. AIME, 
V. 38, 1907, pp. 320-343. 

3. Plyn, J. The Joplin District. 
Mines and Miner., v. 24, Feb. 1904, 
pp. 329-330. 



Kansas, and Oklahoma. 
1972, 362 pp. 



Univ. OK Press, 



4. Norris, J. D. AZn: A 
the American Zinc Company. 
Soc. WI, 1968, 244 pp. 



History of 
State Hist. 



5. Crane, W. R. Methods of Prospect- 
ing, Mining and Milling in Kansas Lead 
and Zinc District. KS Geol. Surv. , v. 8, 
1901, pp. 177-387. 

6. Henri ch, C. Zinc-Blende Mines and 
Mining Near Webb City, Mo. Trans. AIME, 
V. 21, 1892-93, pp. 3-24. 

7. Gibson, A. M. Wilderness Bonanza - 
The Tri-State District of Missouri, 



8. McCauley, J. R. , L. L. Brady, and 
F. W. Wilson. A Study of Stability 
Problems and Hazard Evaluation of the 
Kansas Portion of the Tri-State Min- 
ing Area (contract J0100131, KS Geol. 
Surv. -Univ. KS). BuMines OFR 75-83, 1983, 
193 pp. 

9. McFarland, M. C, and J. C. Brovm. 
Study of Stability Problems and Hazard 
Evaluation in the Missouri Portion of the 
Tri-State Mining Area (contract J0100132, 
MO Dept. Nat. Resour. , Div. Geol. and 
Land Surv.). BuMines OFR 97-83, 1983, 
141 pp. 

10. Luza, K. V. A Study of Stability 
Problems and Hazard Evaluation of the 
Oklahoma Portion of the Tri-State Mining 
Area (contract J0100133, OK Geol. Surv.- 
Univ. OK.). BuMines OFR 76-83, 1983, 
147 pp. 



H 3U^ 85 



INT.-BU.OF MIN ES,PGH.,P A. 27773 



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